Solitary rectal ulcer syndrome (SRUS) is a rare, benign rectal condition with a reported annual incidence of approximately one in 100,000. Despite its non-malignant nature, SRUS can be difficult to diagnose accurately due to its non-specific clinical presentation and similarities to rectal cancer on imaging and endoscopy. Patients often present with symptoms such as rectal bleeding, abdominal pain, constipation, straining during defecation and a feeling of incomplete evacuation. These symptoms, combined with endoscopic appearances that may mimic polypoid or mass-like lesions, frequently lead to misdiagnosis. As a result, some patients undergo unnecessary surgical treatments under the assumption of malignancy.
The pathophysiology of SRUS is not fully understood, but it is commonly associated with rectal prolapse and pelvic floor dysfunction, both of which contribute to prolonged straining and mucosal trauma. Historically, SRUS has been under-recognised, and its diagnosis has relied on a combination of clinical, endoscopic, histological and radiological assessments. Among imaging modalities, magnetic resonance imaging (MRI) offers excellent soft tissue contrast, making it a preferred tool for assessing rectal pathology. However, previous MRI studies on SRUS have been limited to isolated case reports, lacking systematic analysis. A recent study aimed to evaluate MRI features of SRUS and identify combinations of findings that can reliably differentiate it from rectal cancer.
Distinctive Clinical Characteristics
A retrospective analysis was conducted involving 30 patients with SRUS diagnosed between January 2015 and December 2021. These cases were compared with a control group of 120 patients diagnosed with rectal adenocarcinoma of pathological stage ≤T2N0, selected in a 1:4 ratio. All patients underwent pelvic MRI and had clinical, endoscopic and histopathological evaluations. The study revealed that SRUS patients were significantly younger, with a mean age of 37 years, compared to 62 years in the rectal cancer group. SRUS patients also had a longer duration of symptoms and significantly lower levels of carcinoembryonic antigen (CEA), a common tumour marker.
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Although SRUS is benign, six out of the thirty patients were initially misdiagnosed with rectal cancer based on MRI findings. These patients exhibited features such as focal bowel wall thickening and involvement of less than 50 mm in length, which are commonly associated with malignant lesions. Therapeutic responses among SRUS patients were varied: one-third responded well to conservative treatment, one-third experienced recurrence after six months and one-third ultimately required surgery due to persistent or worsening symptoms. In contrast, all rectal cancer patients underwent total mesorectal excision as part of their standard treatment protocol.
MRI Findings in SRUS and Comparative Features
MRI features were independently reviewed by two experienced radiologists, with excellent interobserver agreement for most imaging characteristics. SRUS was associated with several distinct features including ulceration, submucosal oedema, high-low mixed or hypointense signal intensity on T2-weighted imaging (T2WI) and layer enhancement. Among SRUS patients, 63.33% exhibited ulceration, 36.67% demonstrated submucosal oedema, and 76.67% showed unrestricted diffusion. High-low mixed intensity on T2WI was the most common signal pattern, observed in over half the patients. In contrast, these features were either absent or significantly less common in the rectal cancer group. Notably, none of the rectal cancer cases showed unrestricted diffusion, hypo- or high-low mixed intensity on T2WI, or layer enhancement.
All SRUS patients had an intact muscularis propria, distinguishing them from cases of more invasive rectal cancer. Cystic submucosal lesions and enlarged mesorectal lymph nodes were uncommon but present in a minority of SRUS cases. The median length of bowel involved in SRUS was significantly greater than in rectal cancer, measuring approximately 51 mm versus 20 mm, respectively.
Diagnostic Value of MRI Feature Combinations
To enhance diagnostic accuracy, combinations of three MRI features were evaluated. Two combinations yielded particularly strong results: (1) unrestricted diffusion, hypo- or high-low mixed intensity on T2WI and layer enhancement; and (2) unrestricted diffusion, hypo- or high-low mixed intensity on T2WI and submucosal oedema. Both combinations achieved an area under the curve (AUC) of 0.97, with 93% sensitivity and 100% specificity. These combinations outperformed single features and combinations of two features.
Importantly, the combination involving submucosal oedema utilised only non-contrast MRI sequences, making it advantageous in settings where gadolinium contrast administration is either undesirable or not routinely performed. This finding aligns with recommendations from the European Society of Gastrointestinal and Abdominal Radiology, which discourage routine contrast use for local rectal cancer staging. The high diagnostic accuracy achieved without contrast enhancement suggests that SRUS can be reliably distinguished from rectal cancer using standard T2WI and diffusion-weighted imaging.
The study demonstrated that specific MRI features, particularly when combined, are highly effective in differentiating SRUS from rectal cancer. The most reliable diagnostic markers include unrestricted diffusion, hypo- or high-low mixed signal intensity on T2WI, and either submucosal oedema or layer enhancement. These findings provide a non-invasive and reproducible approach to distinguish between these two conditions, which can often be confused due to overlapping clinical and endoscopic presentations. Accurate differentiation is essential to prevent misdiagnosis, avoid unnecessary surgeries and ensure appropriate treatment pathways for patients presenting with rectal lesions.
Source: Insights into Imaging
Image Credit: iStock
